The present invention relates generally to transistors, such as transistors with diffused drains used in switching regulators.
Voltage regulators, such as DC to DC converters, are used to provide stable voltage sources for electronic systems. Efficient DC to DC converters are particularly needed for battery management in low power devices, such as laptop notebooks and cellular phones. Switching voltage regulators (or simply “switching regulators”) are known to be an efficient type of DC to DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency input voltage to generate the output DC voltage. Specifically, the switching regulator includes a switch for alternately coupling and decoupling an input DC voltage source, such as a battery, to a load, such as an integrated circuit. An output filter, typically including an inductor and a capacitor, is coupled between the input voltage source and the load to filter the output of the switch and thus provide the output DC voltage. A controller, such as a pulse width modulator or a pulse frequency modulator, controls the switch to maintain a substantially constant output DC voltage.
Double Diffused Drain (DDD) CMOS devices are commonly employed in switching regulators. DDD devices achieve high voltage tolerance through the introduction of a thick gate oxide and a resistive implant at the drain. The voltage rating of the device is determined by both the gate length and the spacing between the drain contact and the gate; thus establishing a trade-off between voltage rating and device performance.
As the complexity of integrated circuits and the power requirements for portable devices grow, there will be increasing pressure for switching regulators with extremely high efficiency. Therefore it would be advantageous to develop a switching regulator with diffused drains that operates with increased efficiency.